Hammer of the Emperor, a supplement for Only War, is a handbook for the brave soldiers of the Imperial Guard. New options for regiment creation and mixed regiments, along with details on renowned regiments like the Attilan Rough Riders and Tanith First-and-Only, give players unique ways to wage war in the 41st Millennium. Plus, enhance your missions with new Advanced Specialties, an expanded armoury, rules for Mounted Combat, and much more!